The primary purposes of the study are: 1) to compare the effectiveness of lithium carbonate, imipramine, placebo, and a combination of lithium and imipramine in the long-term maintenance treatment of unipolar recurrent affective illness; and 2) to compare the effectivness of lithium, imipramine, and a combination of lithium and imipramine in long-term maintenance treatment of bipolar recurrent affective illness. The study will involve the collaborative effort of four to six centers. Approximately 400 paitents will be studied over a two-year period.